(1) Field of the Invention
The present invention pertains to a load supporting device for use with conventional wheelchair frames. More particularly, the present invention pertains to a wheelchair seat which is adjustable to fit most conventional wheelchair frames and to accommodate different sized wheelchair patients.
(2) Description of the Related Art
In a conventional wheelchair, a soft "sling" type seat is suspended between spaced apart rails of the wheelchair frame for supporting the weight of the wheelchair user. However, these soft "sling" type wheelchair seats can aggravate many of the health problems suffered by wheelchair users.
Persons who use wheelchairs for extended periods of time may require the use of inflatable wheelchair seat cushions to prevent the formation of decubitus ulcers. Inflatable wheelchair cushions, such as the one disclosed in co-assigned U.S. Pat. No. 5,561,875, serve to distribute the weight of the supported body evenly over the area of the body that is in contact with the cushion. The inflatable cushions are generally placed on top of the wheel chair seat. However, the effectiveness of such inflatable cushions is significantly diminished by the curved configuration of a conventional "sling" type wheelchair seat. Moreover, by stacking an inflatable cushion on top of the "sling" seat, the effective seat height is raised an amount equal to the thickness of the inflatable cushion. This may result in the patient not being able to properly reach the foot plates of the wheelchair. It also raises the center of gravity of the patient.
Attempts have been made to replace the "sling" type wheelchair seat with a flat, rigid seat base which can be suspended low enough between the spaced apart rails of the wheelchair frame to accommodate the thickness of an inflatable cushion. For example, U.S. Pat. No. 4,629,246 of Fulton discloses a rigid wheelchair seat base which is hook mounted onto a wheelchair frame. The seat base can be easily removed to facilitate collapsing of the wheelchair for transportation and storage. However, the seat base disclosed in the Fulton patent is not, under normal circumstances, size-adjustable. Consequently, the seat base must be custom constructed for each individual wheelchair and wheelchair user. This can become expensive, even for a single wheelchair user who may require different seat bases as his or her physical needs change over time.
More recently, attempts have been made to provide size-adjustable wheelchair seat bases which can be adjusted to fit a variety of wheelchair frames and to accommodate the current and changing needs of the wheelchair user. For example, U.S. Pat. No. 5,074,620 of Jay et al. discloses a wheelchair seat base which may be adapted to fit a variety of wheelchair frames and which is adjustable to fit different sized users. However, the means for adjusting the length and width of the seat are quite cumbersome and require the use of tools to accomplish any size adjustment. Moreover, the size-adjustment means are rather limited with the seat base being capable of only a few different sizes.
Another problem that arises when using rigid seat bases that are suspended between the spaced apart rails of the wheelchair frame is limited vertical adjustability. As discussed above, in many circumstances, a patient requires an inflatable wheelchair seat cushion to be placed on top of the wheel chair seat. This requires the that the seat base be suspended lower between the spaced apart rails of the wheelchair frame in order to maintain the same effective seat height. However, in many prior art wheelchair seat structures, the seat base can only be lowered a short distance before the seat base and/or the frame structure that supports the seat base intersect the cross braces or "struts" of the wheelchair frame. Attempts have been made to overcome this problem by providing slots or cut-outs in the seat base or panel to accommodate the presence of such cross braces or "struts". For example, U.S. Pat. No. 4,629,246 of Fulton discloses a wheelchair seat with a rigid base having a pair of slots cut into the side edges of the base plate to accommodate the struts of the wheelchair frame on which the seat is mounted.